The Fuller or Thompson distribution is often used as the design gradation for concrete aggregate or highway engineering base gravel.The polydisperse particle accumulation with fractal properties is easy to form a relatively large bulk density.As an ideal design gra-dation,its mechanism of action is not yet available explained in detail.The bulk density of a variety of particles with fractal gradation under isotropic compression is obtained by using particle discrete element simulation technology.The particles are composed of smooth(frictionless)spherical particles,and the shape of the fractal gradation curve is determined by the interval and fractal dimension indicator controls.On this basis,the correlation between the fractal gradation index and macro and mesoscopic indexes such as bulk density and coordination number is studied.It is concluded that the fractal dimension and the particle size interval have an important influence on the bulk density.When the gradation particle size interval is large,the fractal dimension corresponding to the maximum bulk density is about 2.5,which is similar to the Fuller and Thompson gradation often used in engineering.By studying the coordination number and local packing density at the meso-grain level of the stack,it is concluded that when the fractal dimension is about 2.5,the local ordering and contact distribution of the sample are optimized.The results can provide theoretical guidance for further optimizing the gradation design of crushed stone fillers such as concrete,earth-rock dams or roadbeds.
fractal dimensionparticle gradationdiscrete elementgranular material
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